In the following article, my intention is to point out some aspects of the way in which Fichte describes the general structure of reason in the Wissenschaftslehre 1804. In this regard, I will proceed with an analysis of three fundamental theses on the concept of truth, trying to indicate with it the necessary relation that interconnects the concept of truth with such concepts as unity, self-consciousness and certainty. I hope to show that the project of an absolute grounding of knowledge through intellectual intuition was not at all abandoned by Fichte’s late work, but deepened in its most genuine sense.